It is typically meaning the outlet size of submersible pump thread.

BSPT Rp 6 – Thead Dimensions

Basic Thread Dimensions

* The below values are nomoinal (without tolerances) and are valid for both external and internal threads.

Property	mm	Inch
Nominal Pipe Size (Ø)	6″	…
Pitch (TPI) (P)	11	…
Pitch (Distance) (P)	2.309	0.0909
Thread V half Angle (α)	27.5°	27.5°
Height of sharp V (H)	2.218	0.0873
Thread height (h)	1.479	0.0582
Root/Crest Radius (r)	0.317	0.0125
Major Diameter (D)	163.83	6.45
Pitch Diameter (D2)	162.351	6.3918
Minor Diameter (D1)	160.873	6.3336
Tap Drill Size (Td)	-999	-39.3307
Tolerance onD1, D2 & D3	±0.216	±0.0085

Thread Family	BSPP (G)
Relevant Standards	ISO 7-1, ISO 7-2

Tolerances for all Classes

BSPT Rp 6 (Internal Thread)

Property	Minimum	Maximum
Minor Diameter (D1)	163.614 mm (6.4415 “)	164.046 mm (6.4585 “)
Pitch Diameter (D2)	160.656 mm (6.325 “)	161.089 mm (6.3421 “)

BSPT Rp 6-A (External Higher precision)

Property	Minimum	Maximum
Major Diameter (d)	163.614 mm (6.4415 “)	164.046 mm (6.4585 “)
Pitch Diameter (d2)	160.656 mm (6.325 “)	161.089 mm (6.3421 “)

BSPT Rp 6-A (External Low precision)

Property	Minimum	Maximum
Major Diameter (d)	163.614 mm (6.4415 “)	164.046 mm (6.4585 “)
Pitch Diameter (d2)	160.656 mm (6.325 “)	161.089 mm (6.3421 “)